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Old 07-25-2013, 09:18 PM
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jsun325 jsun325 is offline
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Vacuum Gauge to Tune Carb

I've got a '89 ProStar 190 with a Holley 4160 carb. I know the carb can be tuned without a vacuum gauge but using one intrigues me. I've watched the video on the Holley website on using the gauge. They talk about hooking up the gauge to a full manifold vacuum port. The only vacuum port that I see on my engine is the one going to the PCV value. Is this the one I use? Is there another port that I am not seeing? Any insight is greatly appreciated.
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Old 07-25-2013, 09:54 PM
catamount catamount is offline
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This had me confused at first as well. Every automotive tuning video usually shows a port coming off of the throttle body, which none of us with marine carbs should have.

After careful inspection, I found mine... covered in several layers of paint it may be harder to notice. It is a hex head plug located on the back of the intake manifold here:



(this is not my picture, just something I found on the internet to approximate what you should see)
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Old 07-26-2013, 03:34 PM
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jsun325 jsun325 is offline
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Thanks!
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Old 07-26-2013, 03:58 PM
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SugarLake SugarLake is offline
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Is it OK to disconnect the PVC and use that one when setting idle mixture? I'm not sure if that matters at idle or not. The oil filler cap has a breather so crankcase pressure shouldn't be an issue right?
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Old 07-26-2013, 04:25 PM
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j.mccreight@hotmail.com j.mccreight@hotmail.com is offline
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Yes it is totally okay to connect a vacuum gauge to the pcv port.
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Old 07-26-2013, 04:36 PM
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Quote:
Originally Posted by j.mccreight@hotmail.com View Post
Yes it is totally okay to connect a vacuum gauge to the pcv port.
Should I put a tee in the line or is it OK to just connect to the vacum port and leave the PVC line open?
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Old 07-26-2013, 04:46 PM
catamount catamount is offline
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Just curious, why aren't you guys using the dedicated manifold port?
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Old 07-26-2013, 05:00 PM
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SugarLake SugarLake is offline
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Quote:
Originally Posted by catamount View Post
Just curious, why aren't you guys using the dedicated manifold port?
Just convenience for me. Boats up at the cabin, want to do this tomorrow, and I don't know the thread size of the port to buy a nipple ahead of time. Saves me a 45 minute trip to the hardware store once I'm up there.

I'm assuming it's just a threaded plug in there now. Did yours already have a nipple installed?
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Old 07-26-2013, 06:11 PM
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thatsmrmastercraft thatsmrmastercraft is online now
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Anyone with an aftermarket intake manifold needs to Tee into the PCV line. Not a big deal.
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Old 07-26-2013, 07:21 PM
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j.mccreight@hotmail.com j.mccreight@hotmail.com is offline
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Quote:
Originally Posted by SugarLake View Post
Should I put a tee in the line or is it OK to just connect to the vacum port and leave the PVC line open?
No need for a tee, just leave the hose off the pcv valve and install vacuum gauge hose into pcv hose.
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